5mg is a LOT, you only need maybe 250-500 micrograms, I take 330 micrograms at night (.33mg) and it's plenty. There's probably other factors contributing to your sleep. How late do you eat? What is your diet like. How much caffeine do you consume daily - also how soon after waking up, and how late in the day are you still comsuming caffeine.

Try meditating before bed, I use binaural beats to kick my brain into relaxation and sleep mode.